1. Field of the Invention
This invention relates to a method for denitrating tobacco extract via electrodialysis.
2. Description of the Prior Art
Tobacco contains a number of nitrogen containing substances which during the burning of the tobacco yield various components in the smoke. Removal of some of these smoke components, such as the oxides of nitrogen, is considered desirable.
Nitrate salts, such as potassium, calcium and magnesium nitrates, are a major class of nitrogenous substances which are precursors for nitrogen oxides, especially citric oxide. These nitrate salts are normally found in great abundance in burley tobacco stems and strip and to a lesser degree in flue-cured tobacco stems and in reconstituted tobaccos which utilize these components. Attempts have been made to reduce or remove the nitrate from these tobaccos to bring about a significant reduction in the oxides of nitrogen delivered in their smoke. Among the techniques which have been employed to this end are extraction methods whereby the nitrates are removed from the tobacco material.
In accordance with extraction techniques, tobacco materials are generally contacted with water. In this manner, an extract containing the tobacco solubles including the nitrate salts, is formed. The extract is collected and may be discarded or may be treated to remove the nitrate ions. The denitrated extract may thereupon be reapplied to the fibrous insoluble tobacco material from which it was originally removed.
For example, U.S. Pat. Nos. 4,131,118 and 4,131,117 describe denitration of an aqueous tobacco extract by crystallizing the nitrate as potassium nitrate followed by reapplication of the denitrated extract to the tobacco. In U.S. Pat. No. 3,847,164 denitration of tobacco extracts is effected by means of ion-retardation resins which retard ionic material, specifically potassium nitrate, while non-ionic constituents in the tobacco extracts pass unaffected. In the practice of this method rapid neutralization of the resins results, necessitating plant shutdown for regeneration employing costly chemical treatments.
In addition to denitration, extraction processes are employed to remove other components from tobacco. For example, U.S. Pat. No. 3,616,801 describes a process for improving the tobacco burn properties, smoke flavor and ash by controlling the ion content of the tobacco. In accordance with the process therein disclosed the proportion of metallic ions in an aqueous tobacco extract is adjusted, followed by reapplication of the treated extract to the tobacco. Among the treatments suggested for adjusting the metal ion content are ion exchange and membrane electrodialysis. Removal of potassium ions and their replacement with ammonium, hydrogen, calcium or magnesium ions are particuarly desirable in the practice of this process. Other ions, including nitrate, may also be removed to improve the tobacco properties. In Example 6, substantial quantities of various tobacco solubles, including both nitrate and potassium ions, were removed by means of electrodialysis.
Parent application Ser. No. 127,479, now U.S. Pat. No. 4,253,929 describes nitrate removal from tobacco extract by means of electrodialysis, whereby a substantial reduction in nitrate salts is achieved with minimal loss of other tobacco solubles. It has now been discovered that it is possible to minimize conflicting reactions and salt precipitation in the electrodialysis unit and thus prolong the useful life of the electrodialysis membranes during such denitration.